For many years regulated power supplies and alternating current power amplifiers were developed along two different and well defined paths. Regulated power supplies were mainly unipolar and intended to provide very steady direct current output. Alternating current amplifiers were generally intended to amplify and provide alternating current output which was a faithful copy of the input signals.
With the development of programmable power supplies not only was direct current required at the output but they were also required to provide rapid changes in output and with a minimum of transient distortion. When two power supplies of opposite polarity were combined the basis for bipolar output was established.
Now, the bipolar power supply in an operational mode may be considered either a power supply or a power amplifier. Some of the refinements achieved in the development of operational power supplies now become unique advantages to them as power amplifiers. One notable area where this is true is in the matter of feedback. The uses and capabilities of feedback have become an important feature of operational regulated power supplies.